1. Field of the Invention
This invention relates to the field of photographic silver halide systems and more specifically to the processing of photographic silver halide elements.
2. Description of the Prior Art
Photographic silver halide elements have long been used to record images and are often preferred because they have excellent image reproduction characteristics and high speed. In the field of lithography, a host of varied silver halide elements have been described for this method of reproduction, most of which have the high contrast and density needed to produce the good half-tone dots necessary for this reproduction method. However, most of these elements require a so-called "induction period" during development, which means that there is an initial lag period during which processing is relatively slow prior to infectious development when the high contrast and density are achieved.
In an on-going effort to reduce or eliminate the induction period and thereby make a so-called "rapid access system," it has been observed that rapid access can be achieved, for example, by the addition of hydrazines and derivatives thereof to either the silver halide emulsion or to the developing solutions. It has been preferable to add the hydrazine compounds to the emulsion, however, since the processing thereof can be better controlled. Research Disclosure 23510 (November 1983) presents a summary of the extensive literature on this subject.
Although the use of hydrazine compounds reduced or eliminated the induction period, these systems resulted in a loss of image quality such as lower dot quality, or the image may have a spotted appearance, or so-called "pepper." This is extremely undesirable and there have been numerous attempts in the prior art to reduce the propensity of the hydrazine-containing rapid access lithographic systems to produce pepper.
The developing solutions for elements containing hydrazine compounds typically contain conventional silver halide developing agents such as hydroquinone or derivatives thereof. It is typically necessary to add a super-additive developing agent such as phenidone or metol, for example. These developing solutions are necessarily kept at a fairly high pH which is deleterious to the life expectancy of the solution itself and to the processing equipment. Additionally, these prior art developing solutions tend to be environmentally hazardous and will produce sludge in the developing tanks.
Ruger, U.S. Pat. No. 4,937,160 teaches a novel group of hydrazides which can be used in a manner similar to the prior art hydrazines, but with the advantage of somewhat lower processing pH. Silver halide elements containing these novel hydrazides, however, also suffer from the other disadvantages noted above, such as the appearance of "pepper" and the relative toxicity of the developer solutions. Thus, a more stable processing solution with an even lower pH and a shortened development time has long been sought after by the prior art.
The use of ascorbic acid or its derivatives as developing agents for silver halide elements is known in the prior art. For example, James, J., Amer. Chem. Soc., Jan. 1944 (Communication No. 951 from the Kodak Research Laboratories) states that ascorbic and iso-ascorbic acid can be used as developing agents for silver halide elements. Similarly, U.S. Pat. No. 2,688,549 teaches the use of a developer solution comprising 3-pyrazolidone and ascorbic acid or its sugar analogs. However, these prior art developing solutions were very slow and found little or no commercial success.
Recently, because ascorbic acid and its derivatives are environmentally safer than hydroquinone, there have been attempts to enhance conventional developing solutions by substituting ascorbic acid or erythorbic acid together with salts thereof for hydroquinone. For example, U.S. Pat. No. 5,098,819 discloses a hydroquinone-free and alkali metal hydroxide-free developer solution wherein the developing agent consists of a salt of ascorbic or erythorbic acid either alone or in combination with ascorbic or erythorbic acid. In addition to the environmental advantage of removing hydroquinone from the developer solution, these developing agents are also advantageous because they tend to reduce the sludge commonly found in the developing tanks.
However, a shortcoming of the aforementioned ascorbate-containing developer solutions is that their slow development time make them unsatisfactory for use with rapid access processing, particularly with hydrazine-containing films. The prior art ascorbate developer solutions are much lower in pH (e.g., 9.7-10) and are not formulated for the rapid access processing of hydrazine films. Even if the pH is increased, these ascorbate-containing developers will provide unsatisfactory results.
In the general field of silver halide development and processing it has been conventional to try and improve or accelerate the over-all process. Some of the prior art mentions that so-called polyethylene oxides have been used successfully to achieve this acceleration. Additionally, Haist et al., U.S. Pat. No. 2,685,514, describes and claims the use of certain quaternary ammonium compounds, including 1-.beta.-phenethyl-g-picolinium bromide, to increase the activity of hydrazine-containing developer solutions for direct positive elements. (Direct positive elements are those in which an internal latent image has already been formed.) The hydrazine compounds described by Haist et al. are not similar to those currently used in rapid access, negative-working silver halide elements and, although Haist et al. states that these hydrazine compounds could be incorporated into the emulsion, it was not conventional to do so at that time. Indeed, the Examples and the claims of Haist et al. are specifically limited to developer solutions containing hydrazines. Additionally, the development times for the elements in Haist et al. are all over 1 minute, mostly 2-3 minutes, which is commercially unacceptable for the rapid access systems of today.